Cell Cycle and Mitosis

Question 1

Cell Cycle Overview

Answer 1

• Somatic (body) cells reproduce through growth and division

2 stages:
* Growth stage
* Division Stage
Growth stage (interphase) = cells make new molecules
* Increase in size, spends most of time in interphase
Division stage (mitosis) = DNA molecules copied through DNA replication

Question 2

Growth Stage: Interphase

Answer 2

Interphase consists of:

G1 (Growth Phase 1) = cells prepare for synthesis phase by undergoing metabolic processes
* This makes sure cell has enough material to replicate

S Phase (Synthesis) = DNA is replicated/copied

G2 (Growth Phase 2) = cells preparing for division
* Checking for replication errors repairing damage

Question 3

Mitosis

Answer 3

**Mitosis = **division of cell nucleus
* Occurs in all somatic cells

Functions:
* Growth
* Repair
* Maintenance

Cytokinesis = division of cytoplasm

Four stages: prophase, metaphase, anaphase, telophase

Question 4

Phrophase

Answer 4

Early in prophase:
* Chromatin fibres shorten into chromosomes (visible under a light microscope due to density)

Later in prophase:
* Nucleolus disappears
* Nuclear envelope breaks down
* 2 centrosomes begin forming mitotic spindle (assembly of microtubules)

Eventually, spindle fibres extend between two opposite poles of cell

Question 5

Metaphase

Answer 5

• Characterized by the metaphase plate - middle of the cell

Spindle fibres attach to centromere of the sister chromatids
* Pushed towards the metaphase plate/cell equator
* Each chromatid has own spindle fibre

Question 6

Anaphase

Answer 6

• Centromeres split, separating 2 members of each chromatid pair
• Chromatid pairs move to opposite poles of the cell
• When chromosomes are separated they are called chromatids
• Chromosomes pulled by microtubules during anaphase
• Appear to be V shaped because centromeres lead the way, dragging the trailing arms of the chromosomes towards the poles

Question 7

Telophase

Answer 7

• Begins when chromatids have reached the two opposite poles
• Single chromosomes begin to unwind and become less visible

Question 8

Cytokenisis in Cell Division

Answer 8

Separation of cytoplasm
* Formation of two new daughter cells
* Nuclear membrane forms around each new set of chromosomes
* Nucleolus becomes visible
* Cleavage furrow = animal (= the indentation at the center of a dividing cell, which ingresses into a bridge that connects the two daughter cells)
* Cell plate = plant

Question 9

Where are instructions for replication found

Answer 9

Nucleus

Question 10

What do chromosomes hold

Answer 10

Genetic info

Question 11

A chromosome is __ ____ ______ held together by a ______

Answer 11

• 2 sister chromatids
• centromere

Question 12

Chromosome (definition)

Answer 12

One long condensed DNA molecule
* contains 100s of 1000s of genes

Question 13

Chromatin (definition)

Answer 13

mass of very long fibers
* Consists of DNA and protein

Question 14

Autosomes

Answer 14

all the rest of chromosomes (not sex chromosomes), code for other proteins, etc.

Question 15

Chromatids

Answer 15

one of the two identical copies of chromosomes

Question 16

Sister Chromatids

Answer 16

Two identical joined copies of chromosomes

Question 17

Homologous Chromosomes

Answer 17

2 chromosomes of a matching pair, each carrying the same series of genes
* Homologous regions code for the same gene

Question 18

Tetrads

Answer 18

4 chromatids joined together via chiasmata (during crossing over)

Question 19

Human karyotype

Answer 19

human karyotype contains 22 pairs of autosomal chromosomes and a pair of sex chromosomes

Question 20

Sex Chromosomes

Answer 20

The 23rd pair of chromosomes (sex chromosomes) determines gender (boy, girl)
* Female XX
* Male XY
Egg cell contains X, chromosome contains either X or Y